As a cutting insert used for a cutting process performed on a work material, which will be a cut workpiece, a drill described in Japanese Unexamined Patent Application Publication No. 9-029525 (Patent Literature 1) is known. Patent Literature 1 describes a drill having a concave arc-like shape, in a side view, at a front end portion of the body. The drill includes a cutting edge at the arc-like shaped portion.
However, when a cutting process is performed by using the drill having such a configuration, the drill starts to cut into a workpiece, which is an object to be cut, from an outermost periphery of the cutting edge. Thus, the end of the cutting edge comes into contact with the workpiece at a sharp angle. Therefore, the end of the cutting edge may easily chip when the cutting speed is high. During drilling, problems such as chatter vibration or drill deflection may occur. This makes it difficult to improve roundness and positional accuracy of a drilled hole.
In view of the above, it has been desired to have a drill that enables a drilled hole to have a higher positional accuracy and to have a smoother inner wall even when a cutting speed is high.